Integrated oxidative dehydrogenation/carbon filament production process and reactor therefor

ABSTRACT

The present invention includes an integrated process for the production of carbon filaments, comprising converting a portion of hydrocarbons to alkenes via oxidative dehydrogenation and further converting a portion of the alkenes to carbon filaments via contact with a metal catalyst. A portion of unconverted hydrocarbons remaining after oxidative dehydrogenation may also be further converted to carbon filaments via contact with the metal catalyst. The conversion of hydrocarbons to alkenes via oxidative dehydrogenation and further conversion of the alkenes and unconverted hydrocarbons to carbon filaments via contact with a metal catalyst may be carried out in the same or separate reactor vessels. A plurality of reactor vessels arranged in parallel may be used for the conversion of the alkenes and unconverted hydrocarbons to carbon filaments.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims benefit of priority from U.S. Provisional Application Serial No. 60/346,573, filed Jan. 4, 2002, and entitled “Integrated Oxidative Dehydrogenation/Carbon Filament Production Process and Reactor Therefor,” which is incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] Not applicable.

REFERENCE TO A MICROFICHE APPENDIX

[0003] Not applicable.

FIELD OF THE INVENTION

[0004] This invention generally relates to the production of carbon filaments. More specifically, the invention relates to an integrated process employing oxidative dehydrogenation (ODH) to convert alkanes to alkenes (also referred to as olefins) for use as a feedstock in carbon filament production.

BACKGROUND OF THE INVENTION

[0005] Carbon filaments, especially when combined within a polymer matrix to form an engineered composite material, are known for their outstanding physical properties. However, the high cost of manufacturing carbon filaments continues as an impediment to their widespread use, and thus an ongoing need exists for efficient methods for producing carbon filaments.

[0006] Alkanes are saturated hydrocarbons (compounds containing hydrogen [H] and carbon [C]) whose molecules contain carbon atoms linked together by single bonds. The simplest alkanes are methane (CH₄), ethane (CH₃CH₃), and propane (CH₃CH₂CH₃). Olefins, also called alkenes, are unsaturated hydrocarbons whose molecules contain one or more pairs of carbon atoms linked together by a double bond. Generally, olefin molecules are commonly represented by the chemical formula CH₂═CHR, where C is a carbon atom, H is a hydrogen atom, and R is an atom or pendant molecular group of varying composition. Olefins containing two to four carbon atoms per molecule i.e., ethylene, propylene, and butylenes, are gaseous at ordinary temperatures and pressure; those containing five or more carbon atoms are usually liquid at ordinary temperatures.

[0007] Alkanes may be dehydrogenated to form olefins. Olefins have traditionally been produced from alkanes by direct catalytic dehydrogenation processes such as fluid catalytic cracking (FCC) or steam cracking, depending on the size of the alkanes. Heavy olefins are herein defined as containing at least five carbon atoms and are typically produced by FCC. Light olefins are defined herein as containing two to four carbon atoms and are typically produced by steam cracking.

[0008] In the conversion of alkanes to olefins, fluid catalytic cracking and steam cracking (also referred to as thermal cracking) are known to have their drawbacks. For example, the processes are endothermic, meaning that heat is absorbed by the reactions and the temperature of the reaction mixtures decline as the reactions proceed. This is known to lower the product yield, resulting in lower value products. In addition, coke forms on the surface of the catalyst during the cracking processes, covering active sites and deactivating the catalyst. The regeneration cycle is very stressful for the catalyst—temperatures are high and fluctuate and coke is repeatedly deposited and burned off. Furthermore, the catalyst particles are moving at high speed through steel reactors and pipes, where wall contacts and interparticle contacts are impossible to avoid. Catalyst damage and loss are serious problems because the catalysts used in FCC units typically employ precious metals and thus are quite expensive. Further, because FCC and steam cracking units are large and require steam input, the overall processes are expensive even before taking catalyst cost into consideration.

[0009] Oxidative dehydrogenation (ODH) of alkanes to olefins is an alternative to FCC and steam cracking. In ODH, an organic compound is dehydrogenated in the presence of oxygen, typically in a short contact time reactor containing an ODH catalyst. Although oxidative dehydrogenation usually involves the use of a catalyst (referred to herein as an ODH catalyst), and is therefore literally a catalytic dehydrogenation, ODH is distinct from what is normally called “catalytic dehydrogenation” in that the former involves the use of an oxidant, and the latter does not. In the disclosure herein, “oxidative dehydrogenation”, though employing a catalyst, will be understood as distinct from so-called “catalytic dehydrogenation” processes in that the latter do not involve the interaction of oxygen with the hydrocarbon feed. More effective ODH catalysts are highly desirable and thus are under continued development. The capital costs for olefin production via ODH is significantly less than with the traditional processes because of simple fixed bed catalyst reactor designs and high volume throughput. In addition, ODH is an autothermal process, which requires no or very little energy to maintain the reaction. Energy savings over traditional, endothermal processes can be significant, especially through recycling. Also, ODH reactions are comparable in selectivity and conversion to steam cracking.

[0010] Olefins are useful as a feedstock for carbon filament production via catalytic thermal decomposition. In a typical process, filaments are produced by the thermal decomposition of hydrocarbon gas on catalysts comprising metals such as iron, cobalt, and nickel. The hydrocarbon gas is contacted with the metal catalyst at a temperature in the range of about 500 to 900° C., wherein the hydrocarbon gas decomposes and resultant carbon filaments grow. Carbon filaments produced from catalytic decomposition of hydrocarbons may have a wide variety of diameters (from tens of angstroms to tens of microns) and structures (e.g., twisted, straight, helical, branched, and mixtures thereof). The following references, each of which is incorporated herein in its entirety, contain additional disclosure regarding the formation of carbon filaments: Baker et al, The Formation of Filamentous Carbon, Chemistry and Physics of Carbon Vol. 14, p. 83, Marcel Dekker, NY (1978); Baker, Catalytic Growth of Carbon Filaments, Vol. 27, No. 3, pp. 315-23 (1989); Tibbetts, Vapor Grown Carbon Fibers, NATO ASI Series E: Applied Sciences, Vol. 177, pp. 73-94 (1989); and Bokx et al, The Formation of Filamentous Carbon on Iron and Nickel Catalysts, Parts I-III, Journal of Catalysis, Vol. 96, pp. 454-90 (1985).

[0011] It has been found that ODH reaction conditions (and olefins produced there from) are particularly well suited for integration with carbon filament formation to achieve an efficient, integrated process according to the present invention. In terms of product composition, products exiting the ODH catalyst contain primarily olefins and hydrogen with small amount of CO, CO₂ and alkanes, of which the olefins form a preferred precursor for the carbon filament growth. In terms of energy integration, ODH reactions result in exit gas temperatures of 800-1200° C., which decrease to the preferred range of 500-900° C. by optimizing the location of the carbon filament catalyst downstream of the ODH catalyst. Thus, no separate heat input is needed for the carbon filament growth. Furthermore, traditional olefin production processes are endothermic and any subsequent (downstream) processes that require heat input are expensive and so, avoided. This is especially true for carbon filament production, which usually proceeds by pyrolysis of hydrocarbons (mostly alkanes) at higher temperatures. In contrast, an integrated process according to the present invention is a novel, exothermal process.

SUMMARY OF THE INVENTION

[0012] The present invention includes an integrated process for the production of carbon filaments, comprising converting a portion of hydrocarbons to alkenes via oxidative dehydrogenation and further converting a portion of the alkenes to carbon filaments via contact with a metal catalyst. A portion of unconverted hydrocarbons remaining after oxidative dehydrogenation may also be further converted to carbon filaments via contact with the metal catalyst. The conversion of a portion of hydrocarbons to alkenes via oxidative dehydrogenation and further conversion of a portion of the alkenes and unconverted hydrocarbons to carbon filaments via contact with a metal catalyst may be carried out in the same or separate reactor vessels. A plurality of reactor vessels arranged in parallel may be used for the conversion of the alkenes and unconverted hydrocarbons to carbon filaments. Hydrogen and carbon monoxide produced during the oxidative dehydrogenation of the hydrocarbons may be recovered as product gases. Hydrocarbons remaining unconverted following initial oxidative dehydrogenation may be recycled and subjected to further oxidative dehydrogenation. Likewise, any alkenes and unconverted hydrocarbons remaining unconverted following initial contact with a metal catalyst may be recycled and subjected to further contact with the metal catalyst. The integrated process may further comprise graphitizing the carbon filaments.

[0013] The present invention further includes a reactor for the conversion of alkanes to carbon filaments, comprising a reactor vessel having an oxidative dehydrogenation reaction zone and carbon filament reaction zone downstream thereof. The oxidative dehydrogenation reaction zone further comprises a bed of oxidative dehydrogenation catalysts and the carbon filament reaction zone further comprises a metal catalyst. The present invention further includes an integrated process unit for the conversion of alkanes to carbon filaments, comprising an oxidative dehydrogenation reactor wherein alkanes are converted to alkenes and a carbon filament reactor wherein alkenes from the oxidative dehydrogenation reactor are converted to carbon filaments.

DESCRIPTION OF DRAWINGS

[0014] The invention, together with further advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings in which:

[0015]FIG. 1 is a process flow diagram of the present invention.

[0016]FIG. 2 is a process flow diagram of a preferred embodiment of the present invention.

[0017]FIGS. 3 and 4 are scanning electron microscopy (SEM) photos of carbon filaments produced according to the present invention.

[0018]FIGS. 5 and 6 are transmission electron microscopy (TEM) photos of carbon filaments produced according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Referring to FIG. 1, feed stream 5 comprising hydrocarbons and feed stream 7 comprising oxygen are fed to ODH reactor 10, wherein a portion of the hydrocarbons undergo oxidative dehydrogenation in the presence of an ODH catalyst to produce effluent stream 15 comprising CO, CO₂, H₂, H₂O, olefins, and unconverted hydrocarbons. Product gases may be separated and recovered. For example, H₂ and CO may be separated by a separator (not shown), recovered via stream 35, and used in other industrial processes. Hydrocarbon conversion within the CF reactor typically is less than 100 percent in a single pass, and thus the unconverted hydrocarbons may optionally be separated by a separator (for example, a hydrocarbon splitter, not shown) and recycled via stream 30, preferably following removal of H₂ and CO, if applicable. Alternatively, the unconverted hydrocarbons may be fed to the CF reactor as discussed below.

[0020] Hydrocarbons and oxygen may be fed to the ODH in separate streams as shown or may be combined into a single feed stream. Oxygen may be fed to the ODH reactor as pure oxygen, air, oxygen-enriched air, oxygen mixed with a diluent, and so forth. The hydrocarbon feedstock may be any gaseous hydrocarbon having a low boiling point, such as ethane, natural gas, associated gas, or other sources of light hydrocarbons having from 1 to 10 carbon atoms. In addition, hydrocarbon feeds including naphtha and similar feeds may be employed. The hydrocarbon feedstock may be a gas arising from naturally occurring reserves of ethane which contain carbon dioxide. Preferably, the feed comprises at least 50% by volume light alkanes (≦C₁₀).

[0021] Any suitable reactor configuration may be employed in order to contact the reactants with the ODH catalyst. One suitable configuration is a fixed catalyst bed, in which the ODH catalyst is retained within a reaction zone in a fixed arrangement. ODH catalysts may be employed in the fixed bed regime using fixed bed reaction techniques well known in the art. Preferably, a short-contact time reactor (SCTR) is used, for example a millisecond contact time reactor of the type used in synthesis gas production. A general description of major considerations involved in operating a reactor using millisecond contact times is given in U.S. Pat. No. 5,654,491, which is incorporated herein by reference. Additional disclosure regarding suitable ODH reactors and the ODH process is provided in Schmidt et al, New Ways to Make Old Chemicals, Vol. 46, No. 8 AIChE Journal p.1492-95 (August 2000); Bodke et al, Oxidative Dehydrogenation of Ethane at Millisecond Contact Times: Effect of H ₂ Addition, 191 Journal of Catalysis p. 62-74 (2000); Iordanoglou et al, Oxygenates and Olefins from Alkanes in a Single-Gauze Reactor at Short Contact Times, 187 Journal of Catalysis P. 400-409 (1999); and Huff et al, Production of Olefins by Oxidative Dehydrogenation of Propane and Butane over Monoliths at Short Contact Times, 149 Journal of Catalysis p. 127-141 (1994), each of which is incorporated by reference herein in its entirety.

[0022] Within ODH reactor 10, the hydrocarbon feedstock is contacted with the ODH catalyst as a gaseous phase mixture with an oxygen-containing gas in a reaction zone that is maintained at conversion-promoting conditions effective to produce the effluent stream 15 comprising olefins. The process is operated at atmospheric or super atmospheric pressures, the latter being preferred. The pressures may be from about 100 kPa to about 12,500 kPa, preferably from about 130 kPa to about 5,000 kPa. The process of the present invention may be operated at catalyst temperatures of from about 400° C. to about 1200° C., preferably from about 500° C. to about 900° C. The hydrocarbon feedstock and the oxygen-containing gas are preferably pre-heated before contact with the ODH catalyst. The hydrocarbon feedstock and the oxygen-containing gas are passed over the ODH catalyst at any of a variety of space velocities.

[0023] Gas hourly space velocities (GHSV) for the process, stated as normal liters of gas per liters of catalyst per hour, are from about 20,000 to at least about 100,000,000 hr⁻¹, preferably from about 50,000 to about 50,000,000 hr⁻¹, and more preferably from about 50,000 to about 5,000,000 hr⁻¹. Residence time is inversely proportional to space velocity, and high space velocity indicates low residence time on the catalyst. In a preferred millisecond contact time reactor, the reactant gas mixture residence time with the ODH catalyst is no more than about 100 milliseconds.

[0024] ODH catalysts may be of any suitable form, including foam, monolith, gauze, noodles, spheres, pills or the like, for operation at the desired gas velocities with minimal back pressure. Typically, ODH catalysts contain a precious metal, such as platinum, which promotes alkane conversion to alkenes. For example, U.S. Pat. No. 6,072,097 and WO Pub. No. 00/43336 describe the use of platinum and chromium oxide-based monolith ODH catalysts for ethylene production with SCTRs; U.S. Pat. No. 6,072,097 describes the use of Pt-coated monolith ODH catalysts for use in SCTRs; and WO Patent No. 0043336 describes the use of Cr, Cu, Mn or this mixed oxide-loaded monolith as the primary ODH catalysts promoted with less than 0.1% Pt, each of these references being incorporated herein in their entirety. Alternative ODH catalysts are available that do not contain any unoxidized metals and are activated by higher preheat temperatures. Examples of preferred alternative ODH catalysts that do not contain any unoxidized metal are disclosed in copending U.S. Pat. Applications 60/309,427, filed Aug. 1, 2001 and entitled “Oxidative Dehydrogenation of Alkanes to Olefins Using an Oxide Surface” and 60/324,346, filed Sep. 24, 2001 and entitled “Oxidative Dehydrogenation of Alkanes to Olefins Using Non-Precious Metal Catalyst”, which are incorporated by reference herein in their entirety.

[0025] In a preferred embodiment of the present invention, light alkanes and pure O₂ are converted to the corresponding light olefins in a short-contact time reactor employing a metal oxide ODH catalyst.

[0026] In some embodiments, ODH is carried out using the hydrocarbon and/or oxygen feed mixed with an appropriate oxidant, steam, CO₂, or various combinations thereof. Appropriate oxidants may include, but are not limited to I₂, O₂, and SO₂. Use of the oxidant shifts the equilibrium of the dehydrogenation reaction towards complete conversion through formation of compounds containing the abstracted hydrogen (e.g. H₂O, HI, H₂S). Steam may be used to activate the catalyst, remove coke from the catalyst via a water-gas shift reaction, or serve as a diluent for temperature control. CO₂ may be present as part of the source hydrocarbon stream (for example, natural gas) and may be beneficial in serving as a diluent for temperature control and limiting CO₂ production in the ODH reactor.

[0027] According to the present invention, the ODH conversion is integrated with carbon filament (CF) production to achieve an integrated ODH/CF production process. More specifically, effluent stream 15 comprising olefins is fed from the ODH reactor 10 to a CF reactor 20 wherein the olefins are contacted with a metal catalyst and a portion thereof is converted to carbon filaments, which are recovered via stream 25. Effluent stream 15 may further comprise unconverted hydrocarbons remaining following the ODH reaction, in particular in the absence of a hydrocarbon splitter and recycle stream 30 as discussed previously. Like the olefins, the unconverted hydrocarbons are contacted with the metal catalyst and a portion thereof converted to carbon filaments, which are recovered via stream 25. Hydrocarbon conversion within the CF reactor typically is less than 100 percent in a single pass, and thus unconverted hydrocarbons and unconverted olefins from CF reactor 20 may be further processed via recycle stream 32 to the CF reactor.

[0028] The CF catalyst may be any known catalyst for the production of carbon filaments from olefins and/or hydrocarbons, and is preferably a metal catalyst, defined herein as comprising elemental iron, nickel, cobalt, or chromium; alloys comprising the foregoing metals; oxides of the forgoing metals and alloys; and combinations of the foregoing metals, alloys, and oxides. The CF catalyst may comprise any appropriate structure such as a wire, gauze, mesh, sheets, spheres, rods, or coated supports. Preferred CF catalysts include Ni gauzes, a nickel-copper alloy screen or wire known as MONEL® alloy 400 available from Marco Specialty Steel Inc., and a nickel-chromium alloy known as Nichrome® available from Parr Instruments, Inc.

[0029] The CF reactor 20 is configured to support the particular CF catalyst being used and accommodate harvesting of the carbon filaments upon completion of their growth cycle. The CF reactor 20 is further configured such that the carbon filaments can be removed from the metal catalyst and/or reactor vessel. The CF reactor 20 may be either a batch or continuous reactor, and is preferably a continuous reactor, thus allowing the integrated ODH/CF production process to operate continuously. A suitable continuous reactor is shown in FIG. 6 of Tibbetts, Vapor Grown Carbon Fibers, NATO ASI Series E: Applied Sciences, Vol. 177, pp. 78 (1989). Alternatively, one or more reactors such as second carbon filament reactor 40 may be placed in parallel with carbon filament reactor 20, allowing for the integrated ODH/CF production process to operate continuously by switching feed stream 15 between the two reactors as needed for reactor servicing, carbon filament product recovery, etc. While not shown, recycle may be employed with additional reactors as shown and discussed for CF reactor 20.

[0030] As an alternative to separate ODH and CF reactors, a single, combined-process reactor as shown in FIG. 2 may be employed. The combined ODH/CF reactor may be arranged vertically, as shown in FIG. 2, or horizontally. Feed stream 5 comprising hydrocarbons and feed stream 7 comprising oxygen are fed to combined ODH/CF reactor 50. Composition and configuration of the hydrocarbon and oxygen feed streams may be varied as discussed previously with regard to the embodiment shown in FIG. 1.

[0031] The oxygen and hydrocarbon feed come into contact with ODH catalyst bed 52, wherein a portion of the hydrocarbon and oxygen feed is converted to olefins. Upon exiting the ODH catalyst bed, the reactor contents comprise unconverted hydrocarbons and oxygen feed, mixed olefins corresponding to the composition of the hydrocarbon feedstream, hydrogen, carbon monoxide, carbon dioxide, and water. A CF catalyst 54 is positioned in the reactor downstream from the ODH catalyst bed. As the reactor contents flow through the reactor, the olefins produced in the ODH catalyst bed and unconverted hydrocarbons come into contact with the CF catalyst, resulting in carbon filament growth thereon. Carbon filaments are removed from the reactor via carbon filament product stream 56. The carbon filaments may be removed as a continuous operation, or two or more batch type ODH/CF reactors can be employed in parallel, with carbon filament production and recovery alternating among the reactors as described previously to maintain a continuous CF production process. Downstream from the CF catalyst, the reactor contents exit the reactor via effluent stream 58 and comprise unconverted hydrocarbon and oxygen feed, mixed olefins (if any remain following conversion to carbon filaments), hydrogen, carbon monoxide, carbon dioxide, and water. Prior to exiting the ODH/CF reactor 50, the reactor contents are optionally quenched (i.e., rapidly cooled), for example though use of a cooling jacket 60. Unconverted hydrocarbons and unconverted olefins (if any) in effluent stream 58 may be further processed via recycle stream 62. Optionally, product gases such as H₂ and CO may be recovered from effluent stream 58 via a separation process (not shown) located either upstream (i.e., in line 58 a) or downstream (i.e., in line 58 b) of the recycle stream 62, as appropriate.

EXAMPLES

[0032] The examples were carried out using a bench scale combined ODH/CF reactor of the type shown in FIG. 2 and configured without a recycle. The reactor comprised a 0.5 inch inside diameter quartz tube approximately 18 inches in length and arranged vertically with a single hydrocarbon/oxygen feed stream into the top and an effluent stream exiting the bottom. An ODH catalyst bed was positioned in the upper third of the reactor near the feed inlet and a CF catalyst was positioned near the middle of the reactor, downstream of the ODH catalyst bed. The bottom third of the reactor, below the CF catalyst, was cooled with a cooling jacket. The ODH catalyst used was a platinum/gold catalyst. The CF catalyst used was a nickel-copper alloy screen or wire known as MONEL® alloy 400 available from Marco Specialty Steel Inc. The wire was looped back and forth into a bundle and held in place by friction against the reactor walls. A preferred feed to the reactor consisted essentially of a combined ethane and pure oxygen stream of about 4-5 normal liters per minute, resulting in ethylene as a preferred olefin following the ODH reaction. Preferably, the feed stream was preheated to about 150-300° C. before entering the reactor. Temperatures across the ODH catalyst bed ranged from about 800 to 1000° C. upon the ODH reaction being lit off. Temperatures across the CF catalyst ranged from about 500 to 900° C., and preferably about 600 to 800° C. The pressure within the reactor was about 4 psig, with minimal (i.e., less than about 1 psig) pressure drop across the reactor. The reactor was typically run in cycles of about 4-8 hours following the ODH reaction being lit off, resulting in typical yields of about 1-2 g of carbon filaments. The carbon filaments typically adhered to the CF catalyst and were harvested by removing the bottom fitting from the reactor tube and shaking and/or removing the wire CF catalyst from the reactor. The CF catalyst was optionally polished between cycles with an emery cloth, especially when moderate to heavy tarnish existed on the wire following a cycle. In Examples 1-5, operation of the experimental reactor as described above produced the following results summarized in Table 1: TABLE 1 Carbon Carbon Reactor Fila- Exit Gas Carbon ODH Filament Inlet ment Dry Duration Filament Ethane/O2 N2 Feed GHSV Preheat Growth Temp Pressure Yield Composition Example (hrs) Catalyst Feed Ratio (mol %) (×10⁶ hr⁻¹⁾ Temp (° C.) Range (° C.) (psig) (grams) (mol %) 1 6 Ni—Cr 2.0 16 2.59 350 750 5.3 1.57 H₂ = 31.6 C₂H₂ = 0.59 C₃H₈ = 0.05 C₃H₆ = 0.34 O₂ = 0.33 N₂ = 12.9 CO₂ = 2.2 C₂H₄ = 22.7 C₂H₆ = 5.3 CH₄ = 5.2 CO = 19.2 2 6 Ni—Cr 2.0 10 1.96 350 550-900 4.4 1.15 Not Available 3 7 Ni 2.1 10 1.96 350 500-900 4.1 0.75 H₂ = 30.8 C₂H₂ = 0.64 C₃H₈ = 0.08 C₃H₆ = 0.32 O₂ = 0.24 N₂ = 8.6 CO₂ = 3.3 C₂H₄ = 25.8 C₂H₆ = 8.2 CH₄ = 5.0 CO = 17.0 4 6 Ni 2.0 10 2.44 350 500-900 5.0 0.68 H₂ = 31.9 C₂H₂ = 0.88 C₃H₈ = 0.07 C₃H₆ = 0.32 O₂ = 0.29 N₂ = 8.6 CO₂ = 2.0 C₂H₄ = 25.0 C₂H₆ = 6.2 CH₄ = 5.4 CO = 19.5 5 6 Monel ® 2.0 10 2.44 350 500-900 6.7 1.4 Not Available

[0033] A representative sample of the carbon filaments produced during the experiments had the following physical properties as-synthesized: diameters in the range of about 10-200 nm; length of about 10-20 microns; surface area of about 200-350 m²/g; real density of about 1.9-2.1 g/cc; bulk density of about 0.3-0.34 g/cc; Lc (plane thickness) by XRD of about 3-5 nm; d-spacing of about 0.33-0.35 nm, and physical structures as shown in the electron microscopy photographs of FIGS. 3-6. Following graphitization under nitrogen flow at 2500° F. for 30 minutes, the properties are: diameters in the range of about 10-200 nm; length of about 10-20 microns; surface area of about 25-35 m²/g; real density of about 2.0-2.2 g/cc; bulk density of about 0.32-0.34 g/cc; Lc (plane thickness) by XRD of about 10-14 nm; d-spacing of about 0.34-0.36 nm. As can be seen from FIGS. 3-4, which are SEM photos, the carbon filaments having a variety of physical structures are produced, including straight, twisted, and helical carbon filaments. FIGS. 5 and 6 are TEM photos showing that the carbon filaments may be solid filaments as shown in FIG. 5 or may have a tubular structure (also referred to as carbon nanotubes) as shown in FIG. 6. Carbon filaments produced in accordance with the present invention are useful, for example, in engineered composite materials as described previously.

[0034] While the preferred embodiments of the invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit and teachings of the invention. Reactor design criteria, pendant hydrocarbon processing equipment, and the like for any given implementation of the invention will be readily ascertainable to one of skill in the art based upon the disclosure herein. The embodiments described herein are exemplary only, and are not intended to be limiting. Many variations and modifications of the invention disclosed herein are possible and are within the scope of the invention. Accordingly, the scope of protection is not limited by the description set out above, but is only limited by the claims which follow, that scope including all equivalents of the subject matter of the claims. 

What is claimed is:
 1. An integrated process for the production of carbon filaments, comprising converting a portion of hydrocarbons to alkenes via oxidative dehydrogenation and further converting a portion of the alkenes to carbon filaments via contact with a metal catalyst.
 2. The integrated process of claim 1 further comprising converting a portion of unconverted hydrocarbons remaining after oxidative dehydrogenation to carbon filaments via contact with the metal catalyst.
 3. The integrated process of claim 2 wherein the hydrocarbons comprise greater than about 50% light alkanes.
 4. The integrated process of claim 3 wherein the hydrocarbons consist essentially of light alkanes.
 5. The integrated process of claim 1 wherein the conversion of a portion of the hydrocarbons to alkenes via oxidative dehydrogenation and further conversion of a portion of the alkenes to carbon filaments via contact with a metal catalyst are carried out in the same reactor vessel.
 6. The integrated process of claim 5 further comprising converting an unconverted portion of hydrocarbons remaining after oxidative dehydrogenation to carbon filaments via contact with the metal catalyst.
 7. The integrated process of claim 1 wherein the conversion of a portion of the hydrocarbons to alkenes via oxidative dehydrogenation is carried out in a first reactor vessel and the further conversion of a portion of the alkenes to carbon filaments via contact with a metal catalyst is carried out in a second reactor vessel.
 8. The integrated process of claim 7 further comprising converting an unconverted portion of hydrocarbons remaining after oxidative dehydrogenation to carbon filaments via contact with the metal catalyst.
 9. The integrated process of claim 7 wherein the further conversion of a portion of the alkenes to carbon filaments via contact with a metal catalyst is carried out in a plurality of reactor vessels arranged in parallel.
 10. The integrated process of claim 8 wherein the further conversion of a portion of the alkenes and a portion of hydrocarbons remaining after oxidative dehydrogenation to carbon filaments via contact with a metal catalyst is carried out in a plurality of reactor vessels arranged in parallel.
 11. The integrated process of claim 1 wherein hydrogen and carbon monoxide produced during the oxidative dehydrogenation of the hydrocarbons are recovered.
 12. The integrated process of claim 2 wherein hydrogen and carbon monoxide produced during the oxidative dehydrogenation of the hydrocarbons are recovered.
 13. The integrated process of claim 5 wherein hydrogen and carbon monoxide produced during the oxidative dehydrogenation of the hydrocarbons are recovered.
 14. The integrated process of claim 7 wherein hydrogen and carbon monoxide produced during the oxidative dehydrogenation of the hydrocarbons are recovered.
 15. The integrated process of claim 9 wherein hydrogen and carbon monoxide produced during the oxidative dehydrogenation of the hydrocarbons are recovered.
 16. The integrated process of claim 1 wherein unconverted hydrocarbons remaining after the oxidative dehydrogenation are recycled and subjected to further oxidative dehydrogenation.
 17. The integrated process of claim 2 wherein unconverted hydrocarbons remaining after the oxidative dehydrogenation are recycled and subjected to further oxidative dehydrogenation.
 18. The integrated process of claim 5 wherein unconverted hydrocarbons remaining after the oxidative dehydrogenation are recycled and subjected to further oxidative dehydrogenation.
 19. The integrated process of claim 7 wherein unconverted hydrocarbons remaining after the oxidative dehydrogenation are recycled and subjected to further oxidative dehydrogenation.
 20. The integrated process of claim 9 wherein unconverted hydrocarbons remaining after the oxidative dehydrogenation are recycled and subjected to further oxidative dehydrogenation.
 21. The integrated process of claim 1 wherein unconverted alkenes, unconverted hydrocarbons, or both remaining after the contact with the metal catalyst are recycled and subjected to further contact with the metal catalyst.
 22. The integrated process of claim 2 wherein unconverted alkenes, unconverted hydrocarbons, or both remaining after the contact with the metal catalyst are recycled and subjected to further contact with the metal catalyst.
 23. The integrated process of claim 5 wherein unconverted alkenes, unconverted hydrocarbons, or both remaining after the contact with the metal catalyst are recycled and subjected to further contact with the metal catalyst.
 24. The integrated process of claim 7 wherein unconverted alkenes, unconverted hydrocarbons, or both remaining after the contact with the metal catalyst are recycled and subjected to further contact with the metal catalyst.
 25. The integrated process of claim 9 wherein unconverted alkenes, unconverted hydrocarbons, or both remaining after the contact with the metal catalyst are recycled and subjected to further contact with the metal catalyst.
 26. The integrated process of claim 16 wherein unconverted alkenes, unconverted hydrocarbons, or both remaining after the contact with the metal catalyst are recycled and subjected to further contact with the metal catalyst.
 27. The integrated process of claim 17 wherein unconverted alkenes, unconverted hydrocarbons, or both remaining after the contact with the metal catalyst are recycled and subjected to further contact with the metal catalyst.
 28. The integrated process of claim 18 wherein unconverted alkenes, unconverted hydrocarbons, or both remaining after the contact with the metal catalyst are recycled and subjected to further contact with the metal catalyst.
 29. The integrated process of claim 19 wherein unconverted alkenes, unconverted hydrocarbons, or both remaining after the contact with the metal catalyst are recycled and subjected to further contact with the metal catalyst.
 30. The integrated process of claim 20 wherein unconverted alkenes, unconverted hydrocarbons, or both remaining after the contact with the metal catalyst are recycled and subjected to further contact with the metal catalyst.
 31. The integrated process of claim 1 further comprising graphitizing the carbon filaments.
 32. A reactor for the conversion of hydrocarbons to carbon filaments, comprising a reactor vessel having an oxidative dehydrogenation reaction zone and carbon filament reaction zone downstream thereof.
 33. The reactor of claim 32 wherein the oxidative dehydrogenation reaction zone further comprises a bed of oxidative dehydrogenation catalysts and the carbon filament reaction zone further comprises a metal catalyst.
 34. An integrated process unit for the conversion of hydrocarbons to carbon filaments, comprising an oxidative dehydrogenation reactor wherein a portion of the hydrocarbons is converted to alkenes and a carbon filament reactor wherein a portion of alkenes from the oxidative dehydrogenation reactor is converted to carbon filaments.
 35. The integrated process unit of claim 34 wherein a portion of hydrocarbons remaining unconverted after oxidative dehydrogenation is converted to carbon filaments via contact with the metal catalyst. 